Laboratory confirmation of Orientia tsutsugamushi (Kawasaki strain) first identified in Hebei province

Objective To investigate the circulation of Orientia tsutsugamushi in Hebei province through the laboratory examination of a suspected scrub typhus case detected in Baoding of Hebei province on July 13, 2017.

Methods The acute phase serum and convalescent phase serum of the case were collected at day 0 and day 14, respectively. The IgG titers of anti-O. tsutsugamushi in serum were analyzed by using indirect immunofluorescence assay (IFA). The genomic DNA was extracted using DNA extraction kit, and Rickettsiales was identified in this sample by amplifying the Rickettsiales 16S rRNA (rrs) and tsa56 genes. Phylogenetic trees were reconstructed using the maximum likelihood (ML) method implemented in PhyML to determine the genotype of the strain.

Results The highest body temperature of the case with fever of unknown origin was 39℃. The detections for serum antibodies of 9 pathogens, including hantavirus, severe fever with thrombocytopenia syndrome virus, dengue virus, Anaplasma sp., Ehrlichiasp., Rickettsia sp., Salmonella typhi and Salmonella paratyphi and O. tsutsugamushi, were conducted, but only the result of O. tsutsugamushi detection was positive. The titers of IgG against O. tsutsugamushi was 1∶64 in the acute phase serum and 1∶256 in the convalescent phase serum. PCR amplification indicated that the rrs sequence from the strain from the case showed high similarity with O. tsutsugamushi(Kawasaki strain) (99.0%). Meanwhile, phylogenetic analysis of the rrs and tsa56 gene sequences revealed that the sequences from the case had a close relationship with Orientia tsutsugamushi(Kawasaki strain).

Conclusion Orientia tsutsugamushi(Kawasaki strain) was identified for the first time in the laboratory in Heibei province.